Too Much of a Good Thing?

The next two weeks of art sales in New York are typically seen by collectors, dealers and auctioneers as a semiannual checkup on the health of the U.S. market. This year's likely diagnosis: bloated.

The spring auctions, which begin on Tuesday and feature Impressionist, modern and contemporary art, have grown to giant proportions. The three major auction houses -- Christie's International, Sotheby's Holdings Inc. and Phillips de Pury...